Waveguide combiner system and method with less susceptibility to glare

ABSTRACT

A system and method for a head up display (HUD) can mitigate glare. The head up display can include a waveguide combiner including an input grating and an output grating and a glare mitigator disposed to prevent glare through the output grating from reaching an eye box. The glare mitigator can be a shade, a diffuser, a dimming element, or other device for mitigating glare. The glare mitigator can be an active or passive glare mitigator.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is related to: U.S. patent application Ser. No.13/892,026, filed on an even date herewith, by Stratton et al., U.S.patent application Ser. No. 13/250,940, filed on Sep. 30, 2011 by Stahlet al., U.S. patent application Ser. No. 13/251,087, filed on Sep. 30,2011 by Brown et al.; U.S. patent application Ser. No. 13/250,858, filedon Sep. 30, 2011 by Brown et al., U.S. patent application Ser. No.13/250,970, filed on Sep. 30, 2011 by Burns et al., U.S. patentapplication Ser. No. 13/250,994, filed on Sep. 30, 2011 by Wood et al.,and U.S. patent application Ser. No. 13/250,621, filed on Sep. 30, 2011by Brown et al., incorporated herein by reference herein in theirentireties and assigned to the assignee of the present application.

BACKGROUND OF THE INVENTION

The present specification relates to displays. More particularly, thepresent specification relates to head up displays (HUDs).

Conventional HUDs are generally large, expensive and difficult to fitinto small airplanes. Often, conventional HUDs rely on large lenses toform adequate field of view and viewing eye box. Compact HUDs are neededfor tactical jets and other small aircraft where space is constrained inthe cockpit. Substrate guided or waveguide HUDs have been proposed whichuse waveguide combiners to preserve eye box size while reducing lenssize. U.S. Pat. No. 4,309,070 issued to St. Leger Searle and U.S. Pat.No. 4,711,512 issued to Upatnieks disclose substrate waveguide HUDSwhere the pupil of a collimating optical system is effectively expandedby the waveguide structure.

Modern cockpits are incorporating large area head down displays (LADs orLAHDDs). The LADs can provide panoramic views and large areas to thedisplay information below the glare shield of the aircraft. However,such LADs do not provide HUD capabilities and require space in thecockpit that is required by conventional HUDs. HUDs which use waveguidecombiners have a smaller size but can be susceptible to glare or sunspotimaging. The susceptibility is increased in glass cockpit environments,such as, those associated with tactical aircraft.

Accordingly, there is also a need for a HUD that is less susceptible toglare and/or sunspot imaging. There is also a need for a low profile HUDwhich is compatible with LADs and has acceptable display performance inenvironments subject to sunlight or other light. There is a need for aHUD that can fit within the cockpit of a tactical aircraft or othersmall aircraft when an LAD is provided in the aircraft and has glaremitigation. Further, there is a need for a compact HUD for use with anLAD. Further still, there is a need for a HUD having a waveguidecombiner that is less susceptible to solar glare and sunspot imaging.

SUMMARY OF THE INVENTION

An exemplary embodiment relates to a head up display (HUD) for providinglight from an image source in a cockpit environment. The head up displayincludes a waveguide disposed at an angle with respect to a top surfaceof a glare shield having a first coupler at a first end and a secondcoupler at a second end. The waveguide is positioned as a combiner andallows viewing of an outside scene and information from the imagesource. The waveguide includes a diffuser disposed between a surface ofthe waveguide and a windshield of the cockpit or between the surface ofthe waveguide and a ceiling of the cockpit.

Another exemplary embodiment relates to a method of providinginformation to a pilot. The method includes providing light associatedwith the information from within a glare shield to an input coupler of asubstrate waveguide, and providing the light associated with theinformation at the input coupler of the substrate waveguide into thesubstrate waveguide by diffraction and diffracting the light associatedwith the information out of the substrate waveguide at an output couplerof the waveguide for reception by the pilot above the glare shield. Themethod also includes diffusing or blocking sunlight before the sunlightstrikes on a surface of the substrate waveguide at a location associatedwith the output coupler.

Another embodiment relates to a head up display including a waveguidecombiner and a glare mitigator. The waveguide combiner includes an inputgrating and an output grating. The glare mitigator is disposed toprevent glare through the output grating from reaching an eye box.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments are hereafter described with reference to theaccompanying drawings, wherein like numerals denote like elements; and:

FIG. 1 is a general schematic block diagram of a head up display (HUD)system including a substrate waveguide with an input and output couplerand a glare mitigator in accordance with an exemplary embodiment;

FIG. 2 is a general schematic block diagram of a head up display systemincluding a substrate waveguide with an input and output coupler and anactive glare mitigator in accordance with another exemplary embodiment;

FIG. 3 is a side view schematic drawing of an embodiment of the HUDsystems illustrated in FIGS. 1 and 2 in accordance with yet anotherexemplary embodiment;

FIG. 4 is a side view schematic drawing of another embodiment of the HUDsystems illustrated in FIGS. 1 and 2 in accordance with still anotherexemplary embodiment;

FIG. 5 is side view schematic drawing of yet another embodiment of theHUD systems illustrated in FIGS. 1 and 2 in accordance with anotherexemplary embodiment;

FIG. 6 is a side view schematic drawing of a HUD system exposed tosunlight without glare mitigation; and

FIG. 7 is a side view schematic drawing of an exemplary embodiment ofthe HUD systems illustrated in FIGS. 1 and 2 exposed to sunlight withglare mitigation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before describing in detail the particular improved system and method,it should be observed that the invention includes, but is not limitedto, a novel structural combination of optical components and not in theparticular detailed configurations thereof. Accordingly, the structure,methods, functions, control and arrangement of components have beenillustrated in the drawings by readily understandable blockrepresentations and schematic drawings, in order not to obscure thedisclosure with structural details which will be readily apparent tothose skilled in the art, having the benefit of the description herein.Further, the invention is not limited to the particular embodimentsdepicted in the exemplary diagrams, but should be construed inaccordance with the language in the claims.

With reference to FIG. 1, a head up display (HUD) system 10 can beutilized in various applications, including but not limited to aviation,medical, naval, targeting, ground based, military, etc. HUD system 10 ispreferably configured for use in smaller cockpit environments and yetprovides an appropriate field of view and eye box for avionicapplications. In one embodiment, HUD system 10 is configured for use ina tactical cockpit and is compatible with large area head down displays(LADs).

HUD system 10 includes an image source 20 and a substrate waveguidecombiner 40 in one embodiment. Image source 20 can be any device forproviding an image including but not limited to a CRT display, an LEDdisplay, an active matrix liquid crystal display (LCD), a light emittingdiode, laser illuminator, etc. In a preferred embodiment, image source20 is a micro LCD assembly or liquid crystal on silicon (LCOS) displayand can provide linearly polarized light. Image source 20 can include alaser or LED backlight.

In addition, system 10 can include collimating optics 30 disposedbetween substrate waveguide combiner 40 and image source 20. Collimatingoptics 30 can be a single optical component, such as a lens, or includemultiple optical components. In one embodiment, collimating optics 30are configured as a catadioptric collimator. Collimating optics 30 canbe any optical component or configuration of optical components thatprovide light (preferably collimated light) from image source 20 tosubstrate waveguide combiner 40. Collimating optics 30 can be integratedwith or spaced apart from image source 20 and/or substrate waveguidecombiner 40.

In operation, system 10 provides images from image source 20 to a pilotor other operator so that the pilot can simultaneously view the imagesand a real world scene. The images can include graphic and/or textinformation (e.g., flight path vector, target icons, etc.) related toavionic information in one embodiment. In addition, the images caninclude synthetic or enhanced vision images. In one embodiment,collimated light representing the image from image source 20 is providedon substrate waveguide combiner 40 so that the pilot can view the imageconformally on the real world scene through substrate waveguide combiner40. In one embodiment, waveguide combiner 40 is preferably transparentfor viewing the real world scene through main surfaces or sides 84 and88. In one embodiment, waveguide combiner 40 can be bent as discussedbelow with reference to FIG. 5.

In one preferred embodiment, HUD system 10 is configured to provideuniform luminance and expand the pupil of system 10 in one or more axes(e.g., along a vertical axis). Waveguide combiner 40 can effect singleaxis pupil expansion using an input coupler 42 at an input 72 and anoutput coupler 44 at an output 74 that is configured to provide uniformluminance. The single axis expansion can be on the order of 2 to 7 times(e.g., approximately 4 times in one preferred embodiment). Other ordersof pupil expansion are possible depending upon performance criteria,design parameters, and optical components utilized without departingfrom the scope of the invention.

Couplers 42 and 44 can be gradient coupling gratings that provideexcellent image quality and acceptable brightness in a preferredembodiment. Couplers 42 and 44 are implemented as any type ofdiffractive element (e.g., dichromated gratings, holographic or blazedsurface relief gratings) in one embodiment. Couplers 42 and 44 can beimplemented according to a number of techniques including but notlimited to mechanical reproduction, holographic formation, embossing,casting (e.g., into a polymer resin), or lithography.

Substrate waveguide combiner 40 can be a single glass plate or can bemade from two or more fixed glass plates. Substrate waveguide combiner40 can have a variety of shapes including generally rectangular, oval,circular, tear drop-shaped, hexagonal, rectangular with rounded corners,square-shaped, etc.

In operation, substrate waveguide combiner 40 advantageously receiveslight from image source 20 provided through collimating optics 30 at aninput 72 and provides light to a user at its output 74. Image source 20provides information using a single color of light (e.g., green lightapproximately between 500 and 550 nanometers (nm)). Light provided tosubstrate waveguide 40 is preferably linearly S-polarized or P-polarizedand collimated. Alternatively, other polarization, multiple colors, orother colors at different wavelengths can be utilized without departingfrom the scope of the invention. Optics 30 can have an output disposeddirectly adjacent or attached to coupler 42.

Substrate waveguide combiner 40 preferably performs two operations inone preferred embodiment. First, substrate waveguide 40 is disposed toprovide a medium for transporting light by total internal reflectionfrom input 72 to output 74. Light is reflected multiple times off ofopposing main sides 84 and 88 of substrate 40 as it travels from input72 to output 74. Second, substrate waveguide combiner 40 operates as acombiner allowing the user to view the light from image source 20 atoutput 74 and light from the real world scene through sides 84 and 88.

Light from collimating optics 30 first strikes coupler 42 at input 72 onside 84 of substrate waveguide combiner 40. Coupler 42 diffracts lighttoward the length of combiner 40 so that it travels by total internalreflection to output 74 on side 84. At output 74, coupler 44 diffractsthe light toward the user and out of the substrate waveguide combiner40. Coupler 42 at input 72 preferably has a greater efficiency thancoupler 44 at output 74 in one embodiment.

Couplers 42 and 44 are disposed on respective opposing sides 84 and 88of substrate waveguide 40 in one embodiment. Couplers 42 and 44 can alsobe formed on the same side 84 of or within waveguide combiner 40 in onealternative embodiment. Couplers 42 and 44 can be disposed respectivelyon sides 88 and 84 of waveguide combiner 40, within waveguide combiner40 or both on the same side 88 of waveguide combiner 40 in otheralternative embodiments.

Couplers 42 and 44 are preferably disposed in respective areas that arerectangular in shape and have the same width as each other in oneembodiment. Alternatively, couplers 42 and 44 can have different widths.Coupler 44 has a greater height than coupler 42 in one embodiment.

According to one embodiment, system 10 advantageously includes a glaremitigator 92. Glare mitigator 92 can be a device for blocking, diffusingor dimming light from the environment and preventing such light fromaffecting the view of the pilot through waveguide combiner 40. Forexample, glare mitigator 92 can reduce susceptibility to overheadsunlight conditions which can cause solar glare and sunspot imaging viadiffraction through output grating 74. In one embodiment, glaremitigator 92 is a passive glare mitigation element or layer.Alternatively, mitigator 92 can be an active mitigation element.

In one embodiment glare mitigator 92 is a directional diffuser thatdiffuses the sunlight so that diffracted light is significantly lessbright or non-existent to the pilot's eyes. The sunlight rays arediffused and scattered so that they encounter output diffraction grating74 at incident angles that either (1) diffract away from the eye motionbox or (2) diffract into the eye motion box with significantly lowerintensity. Alternatively, a shading mechanism or a dimming mechanism canprovide glare mitigation. System parameters and design criteria canaffect the placement of mitigator 92.

With reference to FIG. 2, HUD system 10 can be utilized with an activeglare mitigator 94. Active glare mitigator 94 includes a control circuit96, an ambient sensor 98 and an active element 99. Mitigator 94 cansense the sunlight or other interfering light within the cockpit viaambient sensor 98 and respond to levels of the light to shade, dim,block or diffuse the sunlight via active element 99. Active element 99can be a diffusing layer that can actively respond to a signal fromcontrol circuit 96 to provide more diffusion when ambient sunlight canprovide conditions associated with solar glare and sunspot imaging inone embodiment. Alternatively, active element 99 can be a selectabledimmer or a selectable shading device. In one embodiment, attenuation ofsunlight can allow the backlight to be dimmed. Conservation of backlightpower and a contrast ratio of 1.2 to 1 can be achieved with lowerluminance provided by the real world in one embodiment.

Ambient sensor 98 can utilize an existing ambient sensor for system 10.A second prismatic path can be used to provide light to the existingambient sensor. The existing sensor or sensor 93 can characterizesunlight exposure conditions in the environment of HUD system 10. Activeelement 99 can utilize various controlled glare mitigation elements,(e.g., electronic dimmers, optical or mechanical gratings, a diffusivelayer electronically controlled shades, etc.) to prevent solar exposureat critical angles.

Active glare mitigator 94 and glare mitigator 92 can use one or more ofa shading, dimming, blocking or diffusing operation. For example,combinations of shading, dimming, blocking and diffusion can beutilized. System parameters and application criteria including angle ofwaveguide 400, characteristics of diffraction of output grating 74,etc., can affect the placement and characteristics of active element 99and mitigator 92.

Advantageously, mitigators 92 and/or 94 diffuse the light before itstrikes or enters grating 74 in the total field of view (TFOV) in oneembodiment. For example, system 10 can advantageously use a diffuserthat is diffused light in one direction of incidence and is transparentin another range incident angles (e.g., the TFOV as seen by the pilot.)Accordingly, the diffuser diffuses the light so that an unobstructedpath from the sun to waveguide combiner 40 does not allow the sunlightto diffract towards the pilot. Advantageously, HUD system 10 in FIGS. 1and 2 provides the advantages of decreased sunspot brightness andreduced glare while being transparent in the total field of view as seenfrom the pilot.

With reference to FIG. 3, a HUD system 200 that is an embodiment of HUDsystem 10 is comprised of a projector 202 and a waveguide combiner 400similar to waveguide 40. Projector 202 is provided beneath a top surfaceglare shield 210 in one embodiment. Substrate waveguide combiner 400 canbe disposed through a glare shield 210 such that the input end ofsubstrate waveguide 400 is beneath glare shield.

Projector 202 can include image source 20 and collimating optics 30.Image source 20 can include a backlight 212 which can be an LEDbacklight in one embodiment. Image source 20 can also include display214 which can be an active matrix LCD, although other types of imagesources 20 are available according to alternative embodiments.

In one embodiment, projector 202 is an LCOS based system including abeam splitter 252, an LED or laser illuminator 250, and an LCOS displayin the position of display 214. An image shaping lens 254 is providedbetween illuminator 250 and beam splitter 252. Beam splitter 252reflects polarized (e.g., s-polarized) light and provides the light todisplay 214 which selectively rotates the polarization to p-polarizedlight in one embodiment. The p-polarized light is provided through beamsplitter 252 and collimating optics 30.

Collimating optics 30 includes a lens 215, a mirror 216 and a lens 218in one embodiment. Lens 215, mirror 216 and lens 218 are configured toprovide collimated light to coupler 42. Optics 30 can be embodied invarious forms including more or fewer components.

Light from collimating optics 30 advantageously enters waveguide 400beneath glare shield 210 at input coupler 42. Light is provided throughwaveguide combiner 400 in a manner similar to waveguide combiner 40discussed above to output coupler 44 for viewing by the pilot.Preferably, output coupler 44 is entirely disposed above a top surfaceof glare shield 210. Projector 202 and combiner 400 partially beneaththe surface of glare shield 210 provides a compact space saving designthat does not interfere with space for LAD. Although specific componentsare discussed for projector 202, various optical components can beutilized. The collimating optics 30 shown in FIG. 3 are not shown in alimiting fashion. Other collimating systems can be utilized.

HUD system 200 can utilize a diffuser 402 that is disposed substantiallyparallel to the line of sight of the pilot as seen from the designlocation such that obscuration is minimized in one embodiment. Diffuser402 can be at an angle with respect to glare shield 210 according tocertain embodiments. Alternatively, diffuser 402 can be a shade ratherthan a diffuser. The shade can be louvered element. In anotherembodiment, diffuser 402 can be a transparent layer with an active orpassive electrochromic layer. Generally, element 402 can be held byrails attached to combiner 400. The material for element 402 can be adiffusing material or be opaque in one embodiment. Advantageously, theshade or diffuser 402 is relatively thin thereby providing reducedobstruction to the pilot's view. In one embodiment, the diffuser istranslucent. Diffuser 402 can be the active element 91 discussed withreference to FIG. 2. In one embodiment, a diffuser 402 is locatedbetween combiner 400 and a ceiling or cockpit or between windshield orthe cockpit and combiner 400. to provide glare mitigation.

With reference to FIG. 4, HUD system 200 includes a layer 422 providedon waveguide 400. In one embodiment, layer 422 is a diffusive layer.Layer 422 can be made spaced apart from surface 84. In one embodiment,layer 422 can be physically separated and parallel to surface 84. In oneembodiment, layer 422 is disposed between combiner 400 and the ceilingor windshield of the cockpit.

With reference to FIG. 5, a HUD system 500 can have a bent waveguidecombiner configuration. A projector 600 for HUD 500 system includes alaser or LED illuminator 604, a backlight 612, an image source 614, abeam splitter 632, and collimating lens 630. A combiner system 503includes a horizontal waveguide 502 and angled waveguide 508.

Waveguide 508 can include a glare mitigation layer 504 or a glaremitigation element 506 similar to element 402 and layer 422 discussedabove with reference to FIGS. 3 and 4. In one embodiment, layer 504 orelement 506 is located between the ceiling or windshield of the cockpit.

Element 506 can be an opaque shade or be a controlled mechanical orelectrical dimming element. Element 506 can be a louvered system that iselectronically or manually controlled in one embodiment. Layer 504 canbe a diffusing layer in one embodiment.

With reference to FIG. 6, light from sun 702 interacts with HUD system700 and can strike waveguide 704 and be diffracted into the eye motionbox 706 of the pilot. For example, light can be diffracted into the eyemotion box 706 of the pilot if it enters waveguide 704 at an anglesupported by the grating equation given the grating spatial period,index of output coupler 44 and the wavelength of light.

With reference to FIG. 7, a glare mitigator 750 can be utilized toprevent light from sun 702 from reaching eye motion box 706. In oneembodiment, element 750 is a layer which diffuses light so that it isnot diffracted into waveguide 704 at angles where it will reach eyemotion box 706 of the pilot. The angles shown in FIGS. 6 and 7 areexemplary only and are related to the angle of the combiner,characteristics of diffraction of output coupler 44, etc. The angles canbe +13 to −30 or +15-25 degrees in certain specific embodiments, Variousfactors can affect the appropriate placement and characteristics ofelement 99 and mitigator 92 without departing from the scope of theinvention.

It is understood that while the detailed drawings, specific examples,material types, thicknesses, dimensions, and particular values givenprovide a preferred exemplary embodiment of the present invention, thepreferred exemplary embodiment is for the purpose of illustration only.The method and apparatus of the invention is not limited to the precisedetails and conditions disclosed. For example, although specific typesof optical component, dimensions and angles are mentioned, othercomponents, dimensions and angles can be utilized. Various changes maybe made to the details disclosed without departing from the spirit ofthe invention which is defined by the following claims.

What is claimed is:
 1. A head up display for use in a cockpit and forproviding light from an image source, the head up display comprising: awaveguide comprising a first waveguide portion physically coupled with asecond waveguide portion, the first waveguide portion having a first endand disposed under and parallel to a top surface of a glare shield, thesecond waveguide portion having a second end and disposed at an anglewith respect to the top surface of the glare shield, the waveguidehaving a first coupler at the first end and a second coupler at thesecond end, the waveguide positioned as a combiner and allowing viewingof an outside scene and information from the image source, the waveguideconfigured to cause light associated with the information to travel bytotal internal reflection from the first end to the second end, thewaveguide having a glare reducer attached to the second waveguideportion and disposed between a surface of the waveguide and a windshieldof the cockpit or between the surface of the waveguide and a ceiling ofthe cockpit, wherein the glare reducer is a directional diffuserconfigured to diffuse ambient light that enters the cockpit through thewindshield before the ambient light enters the waveguide so that theambient light enters the waveguide and travels through the waveguidetowards the second coupler at an incident angle that causes the ambientlight to diffract away from an eye motion box of a pilot upon exitingthe waveguide, thereby reducing sunspot imaging via diffraction throughthe second coupler.
 2. The head up display of claim 1, wherein the glarereducer is a diffuser spaced apart from the surface of the waveguide. 3.The head up display of claim 2, wherein the diffuser is attached to atop end of the waveguide and extends approximately parallel to the lineof sight from a pilot towards a front of the cockpit.
 4. The head updisplay of claim 1, wherein the first and second couplers arediffractive elements.
 5. The head up display of claim 1, wherein thesecond coupler is disposed entirely above the top surface.
 6. The headup display of claim 1, wherein the waveguide has substantially the samewidth as an exit pupil of collimating optics.
 7. The head up display ofclaim 1, wherein light from the image source enters and leaves thewaveguide on a same side.
 8. The head up display of claim 1, whereinlight from the image source enters and leaves on opposing sides.
 9. Thehead up display of claim 1, further comprising a lens disposed betweenthe waveguide and the image source.
 10. The head up display of claim 1,wherein the first coupler has a greater efficiency than the secondcoupler.
 11. A head up display, comprising: a waveguide combinerincluding a first waveguide portion physically coupled with a secondwaveguide portion, the first waveguide portion having an input gratingand disposed under and parallel to a top surface of a glare shield, thesecond waveguide portion having an output grating and disposed at anangle with respect to the top surface of the glare shield, wherein lighttravels from the input grating to the output grating by total internalreflection; and a glare mitigator disposed to prevent glare through theoutput grating from reaching an eye box, the glare mitigator configuredto diffuse ambient light before the ambient light enters the waveguidecombiner so that the ambient light enters the waveguide combiner andtravels through the waveguide combiner towards the output grating at anincident angle that causes the ambient light to diffract away from aneye motion box of a pilot upon exiting the waveguide combiner, therebyreducing sunspot imaging via diffraction through the output grating. 12.The head up display of claim 11, wherein the glare mitigator is adiffusive layer disposed above the output grating.
 13. The head updisplay of claim 11, wherein the glare mitigator is a shade or adiffuser disposed above a glare shield and not parallel to the waveguidecombiner.
 14. The head up display of claim 11, wherein the glaremitigator includes an ambient sensor and an active element for diffusingsunlight in response to the ambient sensor.